Effect of carrier reshaping and narrow MUX-DEMUX filtering in 0.8 bit/s/Hz WDM RZ-DPSK transmission

Effect of the carrier shape in the ultra high dense wavelength division multiplexing (WDM) return to zero differential phase shift keying (RZ-DPSK) transmission has been examined through numerical optimization of the pulse form, duty cycle and narrow multiplex/de-multiplex (MUX/DEMUX) filtering parameters. © 2007 Springer Science+Business Media, LLC.

Non-periodic quasi-stable nonlinear optical carrier pulses with sliding chirp-free points for transmission at 40 Gbit/s rate

In this paper, we demonstrate the possibility of reaching a quasi-stable nonlinear transmission regime with carrier pulses of 12.5 ps width in multi-channel 40 Gbit/s systems. The quasi-stable pulses that are presented in this work for the first time are not dispersion-managed solitons, and are indeed supported by a large normal span average dispersion and misbalanced optical amplification, and representing a new type of nonlinear carrier.

Gain switched multi-carrier transmitter and pilot tone based receiver for long reach access networks

A novel and cost effective long reach PON downlink scenario is proposed employing a multi-carrier transmitter and pilot tone aided direct detection at the receiver. Error free performance with QPSK and 50km transmission is presented. © 2012 OSA.

A unidirectional scheme for high-fidelity optical-carrier dissemination using phase-modulation, homodyne coherent-detection, and frequency entrainment

We report for the first time an ultra-stable optical-carrier dissemination technique for transmission over a 20km unidirectional fibre link. The optical-linewidth of the recovered carrier matches closely that of the original carrier. © 2014 OSA.

112Gbit/s RF assisted dual-carrier DP-16-QAM in installed and new build WDM applications

The performance of a 112Gbit/s dual-carrier DP-16-QAM channel in various WDM configurations is characterized. Variations of the dispersion map, ROADM count and system length are experimentally evaluated and compared with numerical simulation. © 2012 OSA.

Performance enhancement of asymmetric filtered 40 Gb/s carrier suppressed return to zero-differential phase shift keying receiver in a 50 GHz grid

The authors present the impact of asymmetric filtering of strong (e.g. 35 GHz) optical filters on the performance of 42.7 Gb/s 67% (carrier suppressed return to zero)-differential phase shift keying systems. The performance is examined (in an amplified spontaneous emission (ASE) noise-limited regime and in the presence of chromatic dispersion) when offsetting the filter at the receiver by substantial amounts via balanced, constructive and destructive single-ended detections. It is found that with a slight offset (vestigial side band) or an offset of almost half of the modulation frequency (single-side band), there is a significant improvement in the calculated 'Q'. © The Institution of Engineering and Technology 2013.

Phase noise tolerance study in coherent optical circular QAM transmissions with Viterbi- Viterbi carrier phase estimation

We present a performance evaluation of a non-conventional approach to implement phase noise tolerant optical systems with multilevel modulation formats. The performance of normalized Viterbi-Viterbi carrier phase estimation (V-V CPE) is investigated in detail for circular m-level quadrature amplitude modulation (C-mQAM) signals. The intrinsic property of C-mQAM constellation points with a uniform phase separation allows a straightforward employment of V-V CPE without the need to adapt constellation. Compared with conventional feed-forward CPE for square QAM signals, the simulated results show an enhanced tolerance of linewidth symbol duration product (ΔvTs) at a low sensitivity penalty by using feed-forward CPE structure with C-mQAM. This scheme can be easily upgraded to higher order modulations without inducing considerable complexity.

Multi-band carrier-less amplitude and phase modulation for bandlimited visible light communications systems

Visible light communications is a technology with enormous potential for a wide range of applications within next generation transmission and broadcasting technologies. VLC offers simultaneous illumination and data communications by intensity modulating the optical power emitted by LEDs operating in the visible range of the electromagnetic spectrum (~370-780 nm). The major challenge in VLC systems to date has been in improving transmission speeds, considering the low bandwidths available with commercial LED devices. Thus, to improve the spectral usage, the research community has increasingly turned to advanced modulation formats such as orthogonal frequency-division multiplexing. In this article we introduce a new modulation scheme into the VLC domain; multiband carrier-less amplitude and phase modulation (m-CAP) and describe in detail its performance within the context of bandlimited systems.

Brief report:effects of sensory sensitivity and intolerance of uncertainty on anxiety in mothers of children with autism spectrum disorder

This study examined the relations between anxiety and individual characteristics of sensory sensitivity (SS) and intolerance of uncertainty (IU) in mothers of children with ASD. The mothers of 50 children completed the Hospital Anxiety and Depression Scale, the Highly Sensitive Person Scale and the IU Scale. Anxiety was associated with both SS and IU and IU was also associated with SS. Mediation analyses showed direct effects between anxiety and both IU and SS but a significant indirect effect was found only in the model in which IU mediated between SS. This is the first study to characterize the nature of the IU and SS interrelation in predicting levels of anxiety.

Simultaneous multichannel carrier-suppressed return-to-zero to non-return-to-zero format conversion using a fiber Bragg grating

A novel multichannel carrier-suppressed return-to-zero (CSRZ) to non-return-to-zero (NRZ) format conversion scheme based on a single custom-designed fiber Bragg grating (FBG) with comb spectra is proposed. The spectral response of each channel is designed according to the algebraic difference between the CSRZ and NRZ spectra outlines. The tailored group delays are introduced to minimize the maximum refractive index modulation. Numerical results show that four-channel 200-GHz-spaced CSRZ signals at 40 Gbits/s can be converted into NRZ signals with high Q-factor and wide-range robustness. It is shown that our proposed FBG is robust to deviations of bandwidth and central wavelength detuning. Another important merit of this scheme is that the pattern effects are efficiently reduced owing to the well-designed spectra response.

Mitigation of EEPN in long-haul n-PSK coherent transmission system using modified optical pilot carrier

We present the compensation of the equalization enhanced phase noise (EEPN) in the long-haul n-level phase shift keying (n-PSK) coherent optical transmission system, by employing a scheme of phase modulated optical pilot carrier. © OSA 2013.

Effect of spatial inhomogeneity of charge carrier mobility on current-voltage characteristics in organic field-effect transistors

A semi-quantitative model is put forward elucidating the role of spatial inhomogeneity of charge carrier mobility in organic field-effect transistors. The model, based on electrostatic arguments, allows estimating the effective thickness of the conducting channel and its changes in function of source-drain and gate voltages. Local mobility gradients in the direction perpendicular to the insulator/semiconductor interface translate into voltage dependences of the average carrier mobility in the channel, resulting in positive or negative deviations of current-voltage characteristics from their expected shapes. The proposed effect supplements those described in the literature, i.e., density-dependent mobility of charge carriers, short-channel effects, and contribution of contact resistance.

Cognitive behaviour therapy for mothers of children with food allergy:a case series

Background: Food allergy affects quality of life in patients and parents and mothers report high levels of anxiety and stress. Cognitive Behaviour Therapy (CBT) may be helpful in reducing the psychological impact of food allergy. The aim of this study was to examine the appropriateness and effectiveness of CBT to improve psychological outcomes in parents of children with food allergy. Methods: Five parents (all mothers) from a local allergy clinic requested to have CBT; six mothers acted as controls and completed questionnaires only. CBT was individual and face-to face and lasted 12 weeks. All participants completed measures of anxiety and depression, worry, stress, general mental health, generic and food allergy specific quality of life at baseline and at 12 weeks. Results: Anxiety, depression and worry in the CBT group significantly reduced and overall mental health and QoL significantly improved from baseline to 12 weeks (all p < 0.05) in mothers in the CBT group; control group scores remained stable. Conclusions: CBT appears to be appropriate and effective in mothers of children with food allergy and a larger randomised control trial now needs to be conducted. Ways in which aspects of CBT can be incorporated into allergy clinic visits need investigation.

Impact of the carrier relaxation paths on two-state operation in quantum dot lasers

We study InGaAs QD laser operating simultaneously at ground (GS) and excited (ES) states under 30ns pulsed-pumping and distinguish three regimes of operation depending on the pump current and the carrier relaxation pathways. An increased current leads to an increase in ES intensity and to a decrease in GS intensity (or saturation) for low pump range, as typical for the cascade-like pathway. Both the GS and ES intensities are steadily increased for high current ranges, which prove the dominance of the direct capture pathway. The relaxation oscillations are not pronounced for these ranges. For the mediate currents, the interplay between the both pathways leads to the damped large amplitude relaxation oscillations with significant deviation of the relaxation oscillation frequency from the initial value during the pulse.

Analysis of carrier phase extraction methods in 112-Gbit/s NRZ-PDM-QPSK coherent transmission system

We present a comparative analysis on three carrier phase extraction approaches, including a one-tap normalized least mean square method, a block-average method, and a Viterbi-Viterbi method, in coherent transmission system considering equalization enhanced phase noise. © OSA 2012.